Low-tension sparking plug for



Nov. 4, 1958 L. PERAS 2,859,370

- LOW-TEN N SPARKING PLUG FOR INTERN coulBus N- INES Filed Jan. 19

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United States Patent Ofifice 2,859,370 Patented Nov. 4, 1-958LOW-TENSION SPARKING PLUG FOR INTERNAL COMBUSTION ENGINES Lucien Pras,Billancourt, France, assignor to Re'gie Nationale des Usines Renault,Billancourt, France Application January 2, 1957, SerialNo. 632,089Claims priority, application France January 12, 1956 8 Claims. 01.313-131 It is well-known to technicians thatsparking plugs for internalcombustion engines have been developed in which the sparks are producedby discharging the current delivered from a condenser across arelatively reduced gap of from 0.004 to 0.012" between'the twoelectrodes. This gap is filled by a mass of insulating material and thespark glances off its surface.

Generally, the assembly comprising the electrodes and k the insulator iscalled insert or cartridge.

This invention relates to low-tension sparking plugs and moreparticularly to improvements in the aforesaid inserts for sparking plugsof this character.

These inserts are characterized in that they consist of two metalelectrodes in the form of coaxial hollow cylindxical members, theinterval between these cylinders being kept to a constant value by aninsulating cylinder filling without clearance the gap between theelectrodes. A central hole is provided in the insulator for the dualpurpose of permitting the assembling of the. insert components byclamping and feeding the current to one of the electrodes.

According to another feature of this invention, the sparking surfaces ofthe cylindrical members, which are slanted lie consequently at thedesired distance or space from each other are so machined, before orafter the assembling step, that they diverge radially so that the spacebetween the electrodes is splayed outwardly.

Sparking plugs having this specific configuration, in accordance withthe invention, are characterized by a rig useful life and operateregularly. They are also adtageous in that they avoid completely thefrequent wback of low-tension sparking plugs whereby the k, subsequentto a certain deterioration of the insuor, occurs inside the insert anddoes not ignite the air- 1 mixture.

In the accompanying drawings:

Figure 1 is an axial section showing a first embodiment a sparking pluginsert constructed in accordance with e teachings of this invention;

Figure 2 is a similar view showing a preferred method f assembling thecomponent elements of the device of ig. 1; and

. Figures 3 and 4 are axial sections showing modified ,1 embodiments ofthe invention.

" In the drawing, Figure 1 illustrates, by way of example,

, a typical embodiment of the invention wherein the electrode 1 isconnected to the distributor through the central rod 2; the otherelectrode 3 is earthed through the spark ing plug body (not shown) inwhich it is force fitted or otherwise secured. It will be understoodthat the electrodes may be cylindrical or may have a plurality of flatperipheral surfaces, as for example, they may be prismatic. Theinsulator 4 fills completely the inner space of the two superposed butspaced electrodes, and the sparks occur only on the massive portion 5thereof.

As illustrated, the registering edges of the two cylinders are bevelledto form a gap splayed outwards, so that 2 V the spark will occur on thefree lateral surface of the insulator 4. e

Thisinsulator may consist, for example, of borosilicated glass accordingto the embodiments later herein described. a

In a specific embodiment, it is possible for example, as illustrated inFig. 2, to position the lower electrode 1 into a hollow cylinder 6 ofrefractory steel, with a certain clearance therebetween, andsubsequently introduce the upper electrode 3 for example after havinginterposed between the electrodes three detachable mica segments 7. Theassembling step is completed by an upper cylinder 8 and a core 9 ofrefractory steel or graphite. Then the two electrodes 1, 3 are filledwith glass powder, for example borosilicated glass, and the assembly isheated .to about 1.470 F., whereafter the glassis compacted by exerting.a certain pressure thereon by means of the piston 9 Upon cooling, theinsulating material sets and finally, the insert is ejected, and anyglasshaving been extruded in the sparking gap beyond the insulatorsurface is removed by a proper grinding operation. It will-be understoodthat the mica piecs 7, may be left on or can be removed from theassembled electrodesas desired. These mica segments or pieces 7 are of adimension that does not interfere with the sparking zone of theassembled electrodes.

. Another possible embodiment of the present invention is illustratedinFig.3 of the drawing wherein .the insulator 10 of the insert consists ofa cylindrical body which may be moulded beforehand and accuratelymachined to size; the upper electrode is formed with an inner shoulder11 permitting an arcuate relative spacing of the two electrodes. Y

Asanalternative, the narrowest portion of the spark gap is not defined.by the innercylindrical surface of the electrodes ;but lies atanintermediate'distance between this surface and the outer cylindricalsurface of i the electrodes. This modification is illustrated in Fig. 4.If the insulator consists of a sintered mixture of glass and mica, theinsulator may coincide with the narrowest portion of the spark gap bycoating the lateral surface of the insulator body with powdered glass orlead silicoborate, or one of these powders in suspension in a liquid.Then the assembling step is performed during which the powder or pastefills the space 12, and finally the assembly 1. In a low tension surfacedischarged spark plug, a hollow tubular first electrode, a secondelectrode spaced axially of the first electrode, an insulator coredisposed axially in the first electrode and substantially correspondingin diametral dimensions to the bore thereof and extending axially out ofone end thereof, the second electrode being adapted to receive the endof the insulator core extending axially from the first electrode, saidelectrodes having registering slanted, sparking, end surfaces spacedaxially of each other and diverging radially of the electrodes in adirection away from the longitudinal axis of the first electrode therebydefining a splayed sparking zone, whereby the insulator maintains theelectrodes spaced in a fixed axial relationship.

2. In a low tension surface discharge spark plug according to claim 1,in which the core insulator comprises a sintered glass and mica mixture.

3. In a low tension surface discharge sparkplug according to claim 1, inwhich the electrodes are made of tungsten.

4. In a low tension surface discharge spark plug according to claim 1,in which the insulator core comprises borosilicated glass.

5. In a low tension surface discharge spark. plug, a

first hollow tubular electrode, a second electrode spaced insulatorhaving peripherally 'exposed'surfaces in the space between'the slantedsmracesorthe two electrodes thereby to maintain the two electrodesaxially spaced in fixed relationship. 6. In a low tension surfacedis'charge spark plug, afirst hollow tubular electrode,a'secondelectrode spaced axially of the firstelectrode; an insulatorscore disposed axially in the firstelectrode and extending'axially outof one end thereof, the'second electrode'being adapted to receive theend of the insulator core extending axially frorn t he first electrode,saidelectrodesfhaying' registering slanted, spark ing', end surfacesspaced'axially of each other'an diverging radially of the' electrodes ina direction" away from" the: longitudinal axis ofthe' first electrodethereby defining asplayed' sparking zone, and fnon=condfuctive means disposed in the space"between".the' slanted surfaces of the two electrodesand having'an' outer diameter larger'than the inner diameter of thefirst electrodeiand' said Qatari diameter being smaller than the outerdiameter "of the "first electrode. I

7. In a low tension surface discharge. spark pliigfa hollowtubular'first electrode, ajse'cond electrode spacedaxially of the firstelectrode, an insulator"c'ore disposed axially .in' the first:electrode"substantially corresponding with the' bore thereof andextending axiallyToiit of one i I from the longitudinal axis of, areelectrode end thereof,"thesecond electrode being adapted to e'ceive' theend of the insulator core extending axiau nomthe first electrode, saidelectrodes having registerin'gfslante dj sparking; end surfaces: spacedaxially of each other and divergingradially of thefel'ectrodes' in adirection away" 40 v V 4 defining a splayed sparking zone, and the coreinsulator having aportion having an outer diameter larger than -theinner diameter of the first electrode and said outer diameter beingsmaller than the outer diameter of the 1 first electrode in the spacebetween the slanted surfaces of the two electrodes.

8. -In a low tension surface discharge spark plug, in combination, ahollow tubular first electrode, a second electrode disposed in axiallyspaced relation of the first electrode, an insulator core disposedaxially in the first" electrode and extending axially out ofone endthereof,

the second electrode being adapted to receive the end' of a theinsulator core extending axially from the .fir'st elec-, trode therebyto hold the two electrodes in axially spaced relationship, saidelectrodes having corresponding end, sparking surfaces disposed injuxtaposition axially of each other, said end surfaces of each of theelectrodes being V+shaped and each having the apexthereof. disposedtoward each other; and constitutingsthe point at which there; is the,least axial distance between :the. endcsurfaces, and thecoreinsulatorhavinga portion extending radially, into the, space, defined between.said end surfaces :of the I electrodes, said core portion having a:diametericorrespending substantially to the .diameter, of .theelectrodes betweentwolpoints;wherein the axial distance betweensurfaces; whereby a .'splayed sparking zone isv defined between theelectrodes,,andz.erosion of said coreportion does not impede.thetdi'scharge between said vend .sparking surfaces; atleast until {thecore iserodedto an extent whereinthediameterof, said core portioncorresponds to theIinnerdiameteLof'said first'electrode. a

i References Cited the, file of, patent r UNITEDSTATES-PATENTS 1 .503 Isi i i .--'.-f---..-,-.-.i-r- --f r-1 5, 1

v :FQREIGN rwranrs 14.8907 Australia s Aug, 3,1950.

